Concerned the Superdome might not be able to handle the energy needed for its first Super Bowl since Hurricane Katrina, officials spent hundreds of thousands of dollars on upgrades to decayed utility lines, according to documents obtained by The Associated Press.

The improvements apparently weren't enough, however, to prevent an embarrassing and puzzling 34-minute power outage during the third quarter of the game between the Baltimore Ravens and San Francisco 49ers on Sunday.

Two days later, officials still had not pinpointed the cause of the outage. The Superdome's management company, SMG, and the utility that supplies the stadium, Entergy New Orleans, announced Tuesday that they would hire outside experts to investigate.

"We wanted to leave no stone unturned," Entergy spokesman Chanel Lagarde told the AP. He said the two companies had not been able to reach a conclusion on the cause and wanted a third-party analysis.

"We thought it was important to get another party looking at this to make sure we were looking at everything that we need to examine," Lagarde said.

SMG Vice President Doug Thornton told a news conference at City Hall later Tuesday that the hiring of a third party does not signify a disagreement between SMG and Entergy.

"It's important for us to have total transparency and we have agreed among ourselves that we will exchange records," Thornton said. "We were metering the power. They were doing the same on their side. We need to figure out what the root cause of this is and fix it."

Documents obtained Monday through a records request by The Associated Press show that Superdome officials worried months ago about losing power during the NFL championship.

Tests on the electrical feeders that connect incoming power from utility lines to the stadium showed decay and "a chance of failure," state officials warned in a memo dated Oct. 15. The documents, obtained by the AP through a records request, also show that Entergy expressed concern about the reliability of the service before the Super Bowl.

The memo said Entergy and the Superdome's engineering staff "had concerns regarding the reliability of the Dome service from Entergy's connection point to the Dome."

The memo was prepared for the Louisiana Stadium & Exposition District, the state body responsible for the Superdome.

Authorities subsequently authorized spending nearly $1 million on Superdome improvements, including more than $600,000 for upgrading the dome's electrical feeder cable system, work that was done in December.

"As discussed in previous board meetings, this enhancement is necessary to maintain both the Superdome and the New Orleans Arena as top tier facilities, and to ensure that we do not experience any electrical issues during the Super Bowl," said an LSED document dated Dec. 19.

Superdome commission records show a $513,250 contract to replace feeder cables was awarded to Allstar Electric, a company based in suburban New Orleans.

Arthur Westbrook, Allstar's project manager for the job, referred all questions about possible causes of the outage to the management company.

A lawyer for the LSED, Larry Roedel, said Monday a preliminary investigation found the replacement work done in December did not appear to have caused Sunday's outage.

Eric Grubman, NFL executive vice president of business operations, told the AP on Tuesday that the league was aware of the city's pre-game upgrades to the utility lines, "which we understood to be important and beneficial."

"SMG and others kept us apprised and those reports gave us no real cause for concern," Grubman said. "It is natural and understandable for energy suppliers to be concerned prior to a huge event. If an engineer is asked whether something is 100 percent failsafe, an engineer will normally say, 'No, there is always a risk of failure.'"

Both Entergy and SMG said Sunday that an "abnormality" occurred where stadium equipment intersects with an Entergy electric feed, causing a breaker to create the outage. It remained unclear Monday exactly what the abnormality was or why it occurred.

The lights-out championship game proved an embarrassment for New Orleans just when it was hoping to show the rest of the world how far it has come since Hurricane Katrina in 2005. But many fans were forgiving, and officials expressed confidence that the episode wouldn't hurt the city's hopes of hosting the championship again.

To New Orleans' relief, NFL Commissioner Roger Goodell said the city did a "terrific" job hosting its first pro-football championship in the post-Katrina era.

"I fully expect that we will be back here for Super Bowls," he said, noting a backup power system was poised to kick in but wasn't needed once the lights came back.

Mayor Mitch Landrieu told a news conference Tuesday that the outage won't hurt the city's chances of hosting another Super Bowl and he joked that the game got better after the blackout.

"That 34 minutes is not going to cast a shadow over the accomplishments of the city," Landrieu said, calling the event "as near-perfect a Super Bowl as the country has ever seen." He added that officials estimate the game brought $432 million into the city.

Fans watching from home weren't deterred, either. An estimated 108.4 million television viewers saw the Baltimore Ravens beat the San Francisco 49ers 34-31, making it the third-most-viewed program in television history. Both the 2010 and 2011 games hit the 111 million mark.

As for possible culprits, it couldn't be blamed on a case of too much demand for power.

Meters showed the 76,000-seat stadium was drawing no more electricity than it does during a typical New Orleans Saints game, according to Doug Thornton, the Superdome manager.

He also ruled out Beyonce's electrifying halftime performance. She brought along her own generator.

Officials with the utility and the Superdome were quick to note that an NFL game, the Sugar Bowl and another bowl game were played there in recent weeks with no apparent problems.

Cynthia Hedge-Morrell, chairwoman of the New Orleans City Council's Utility Committee, called an emergency committee meeting Friday with Entergy representatives and others, seeking additional information.

The blackout came after a nearly flawless week of activity for football fans in New Orleans leading up to the big game.

The Big Easy last hosted the Super Bowl in 2002, and officials were hoping this would serve as the ultimate showcase for the city's recovery since Hurricane Katrina in 2005. The storm tore holes in the roof of the Superdome and caused water damage to its electrical systems, and more than $330 million was spent repairing and upgrading the stadium.

Sunday's Super Bowl was New Orleans' 10th as host, and officials plan to make a bid for an 11th in 2018.